1. Field of the Invention
The present invention relates to a running-safety system for an automotive vehicle.
2. Description of the Related Art
Heretofore, there is known an automatic brake system as a running-safety system for an automotive vehicle. For example, Japanese Patent Unexamined Publication (kokai) No. 54(1979)-33,444 discloses an automatic brake system so adapted as to apply braking force to each of the wheels by operating an actuator when the risk of a collision of the body of the vehicle with an obstacle existing ahead in a running way along which the vehicle is running, if the vehicle would run as it does is decided to occur by continually monitoring, for example, a distance between the body of the vehicle and the obstacle with a radar unit. Such a running-safety system includes one of such a type as giving an alarm to a driver prior to an operation of an automatic brake system or of such a type as merely giving an alarm to a driver, in place of an operation of an automatic brake system.
As a system for detecting an obstacle existing ahead in a running way along which the vehicle is running, for example, Japanese Patent Unexamined Publication (kokai) No. 51(1976)-7,892 discloses a system that comprises a radar unit for detecting the obstacle, such as the body of a vehicle running ahead in the running way along which the vehicle is running by transmitting radar waves, such as ultrasonic waves, electrical waves, or the like, forward the obstacle existing ahead and receiving the reflected waves from the obstacle, a pivotal means for pivoting the radar unit horizontally, and a steered-angle detecting means for detecting a steered angle of the wheels of the vehicle. The system is so adapted as to detect the obstacle existing ahead in the running way along which the vehicle is running by directing the radar waves toward the direction in which the vehicle is running by pivoting the radar unit at a given angle with the pivotal means so as to comply with the steered angle of the vehicle detected by the steered-angle detecting means.
Further, systems have been developed which are of such a type as capable of monitoring obstacles existing ahead in a limited range of the running way of the vehicle by scanning a horizontal direction in which the vehicle is running at a relatively wide angle with a radar unit of a scanning type and picking up only the obstacles that can be predicted with a microcomputer from information gathered by scanning of the horizontal direction of the running way in which the vehicle is running, as existing ahead in the running way of the vehicle on the basis of the steered angle.
Such systems, however, suffer from the disadvantage that a detectable distance to be detectable by a detection means such as the radar unit is caused to be reduced to a remarkable extent due to weather situation such as fog, rain, or the like. Further, such a detectable distance in the running way of the vehicle to be detectable by the detection means is reduced due to a so-called blind curve of the running way in which the vehicle is running, which blocks the driver from seeing the curved side of the running way along which the vehicle is running.
As a means for competing with the drawbacks of the conventional systems in case of encountering with the difficulty in finding the obstacle existing ahead in the running way of the vehicle, Japanese Patent Unexamined Publication (kokai) No. 2(1990)-7,156 discloses a system that can stop the control itself for operating an action for avoiding a collision of the body of the vehicle with the obstacle. Patent Unexamined Publication (kokai) No. 53(1978)-16,230 discloses a system that can assume, for example, a distance between the body of the vehicle and an obstacle existing ahead in the running way of the vehicle on the basis of a detected value when the detectable distance is caused to become shorter than in driving the vehicle at usual conditions and then continue making a decision to determine if the body of the vehicle might strike against the obstacle.
However, the system as disclosed in Japanese Patent Unexamined Publication (kokai) No. 2(1990)-7,156 cannot demonstrate the function of a system for avoiding a collision with the obstacle existing ahead in the forward direction along the running way of the vehicle so that the system cannot be said as desirable in terms of ensuring safety in driving the vehicle. On the other hand, the system as disclosed in Japanese Patent Unexamined Publication (kokai) No. 53(1978)-16,230 suffers from the disadvantages that, although it is effective for a short period of time after the point when the detectable distance became shorter, the probability of causing an error in assumption becomes larger as the period of time elapses thereafter and that, if a new obstacle occurs is caused to appear ahead in the forward direction along the running way of the vehicle, the action for avoiding the new obstacle cannot be taken in an effective fashion.
Furthermore, when the vehicle is curved or cornered rapidly at a high speed or at a sharp angle, there may be the occasion that the running way of the vehicle to be predicted may extend toward the outside of a region that can be detected with the radar unit. In this case, the radar unit cannot detect an obstacle even if such an obstacle would exist ahead in the running way of the vehicle; however, there is the risk that the driver makes a wrong decision to that effect that no obstacle exists ahead in the running way of the vehicle because the driver is unaware of the situation that the predicted running way of the vehicle extends outside the detectable region to be detectable by the radar unit.